Austenitic steel generator rings and steel therefor



United States Patent Ofiice 3,062,692 Patented Nov. 6, 1962 I AUSTENITICSTEEL GENERATOR RINGS AND This invention relates to generator rings andsteels therefor capable of developing high yield strengths by coldworking and aging coupled with sufficient ductility to permit largeamounts of cold work and more particularly to generator rings andforgings having such properties along with a grain size no larger thanASTM #4.

So-called generator rings or retaining rings used as coil supports ingenerator rotors must be formed of austenitic, i.e. nonmagnetic, steelsto avoid electrical losses. It is necessary that these rings possesshigh yield point in excess of 125,000 p.s.i. (0.2% offset) which requirethat the rings after forging and heat treating must be warm or coldexpanded 25% or more to develop the required strength limit. These ringsare subjected to rigid inspections because of the serious nature offailure in use. Ultrasonic inspection is one of the preferred types ofinspection but this cannot be used satisfactorily on steels having agrain size larger than ASTM #1.

It is accordingly an object of the present invention to provideaustenitic generator ring steels having a grain size no larger than ASTM#4 along with good hot and cold forging properties.

The foregoing and further objects will be apparent from the followingspecification.

We have discovered that the desired combination of properties can beachieved with a steel composition containing:

.60 to .80% carbon 8.00 to' 10.00% manganese .20 to .60% silicon 6.00 to7.00% nickel 4.00 to 5.00% chromium .30 to .60% eolumbium with thebalance substantially iron and other elements in amounts which are notharmful to the properties.

As a specific example, steel of the following composition was treated inaccordance with our invention:

0.70% carbon 9.00% manganese .035% phosphorus .015% sulphur 0.50%silicon 6.50% nickel 4.25% chromium 0.010% aluminum 0.010% nitrogen0.30% columbium with balance substantially iron.

Ring specimens of this steel were heated to 2000 F. for 2 hours and aircooled. After heating and cooling, the specimens had a grain size of 5-6according to the ASTM chart. One specimen was cold expanded and theother The 30% expanded steel was then Solution temperature:

subjected to an aging treatment at 600 F. for 2 hours. The results wereas follows:

Yield Strength (0.02% offset); p.s.i.

Yield Elonga- Strength Tensile tion in (0.2% Strength, 2 onset), p.s.i.percent p.s.i.

Reduc- Cold Worked, of percent Area,

percent These tests indicate that the steel of our invention may be coldexpanded 25 to 30% to obtain the desired tensile strength and 0.2%offset yield strength. Considerable improvement in the .02% offset yieldis obtained by aging along with minor improvements in .2% offset yield,tensile strength, elongation and reduction of area. The aging should bein the range of 500 to 650 F. for sufficient time to achieve uniformityof temperature.

The grain size above stated is a true inherent grain Size and remainssubstantially the same after difierent solution temperatures as can beseen from the following tabulation.

ASTM grain size 1800 F. 6 2000 F. 22000 F. 46

While we have shown and described one specific embodiment of ourinvention, it will be understood that this embodiment is merely for thepurpose of illustration and description and that various other forms maybe devised within the scope of our invention, as defined in the appendedclaims.

We claim:

1. A cold expanded austenitic steel generator rotor coil supportretaining ring characterized by a grain size no coarser than ASTM #4containing .60 to .80% carbon, 8.00 to 10.00% manganese, .20 to .60%silicon, 6.00 to 7.00% nickel, 4.00 to 5.00% chromium and .30 to .60%eolumbium with the balance iron and other elements in amounts which donot have a harmful effect on the properties.

2. An austenitic steel generator rotor coil support retaining ringcharacterized by a grain size no coarser than ASTM #4 and by having beencold expanded over 25% containing .60 to .80% carbon, 8.00 to 10.00%manganese, .20 to .60% silicon, 6.00 to 7.00% nickel, 4.00 to 5.00%chromium and .30 to .60% eolumbium, balance substantially iron.

3. A method of producing austenitic steel generator rotor coil supportretaining rings characterized by a grain size no coarser than ASTM #4and 0.2% yield strength greater than 125,000 p.s.i. comprising forming aring of steel containing .60 to .80% carbon, 8.00 to 10.00% manganese,.20 to .60% silicon, 6.00 to 7.00% nickel, 4.00 to 5.00% chromium and.30 to .60% columbium, balance substantially iron, and cold expandingsaid ring at least 25 4. A method of producing austenitic steelgenerator rotor coil support retaining rings characterized by a grainsize no coarser than ASTM #4 and 0.2% yield strength greater than125,000 p.s.i. comprising forming a ring of steel containing .60 to .80%carbon, 8.00 to 10.00% manganese, .20 to .60% silicon, 6.00 to 7.00%

a nickel, 4.00 to 5.00% chromium and .30 to .60% columbium, balancesubstantially iron, cold expanding said ring between 25% and 30% andthen aging it at a temperature between 500 and 650 F.

5. An austenitic steel characterized by good cold formability and agrain size no coarser than ASTM #4 containing .60 to .80% carbon, 8.00to 10.00% manganese, .20 to .60% silicon, 6.00 to 7.00% nickel, 4.00 to5.00% chromium and .30 to .60% columbium, balance substantially iron.

6. An austenitic steel characterized by being hardenable by cold workingand aging and having a grain size no coarser than ASTM #4 in thehardened condition,

References Cited in the file of this patent UNITED STATES PATENTS1,561,306 Brace Nov. 10, 1925 1,574,782 Becker Mar. 2, 1926 2,449,023Thornton Sept. 7, 1948 2,859,149 Straumann Nov. 4, 1958 :UNITED STATESPATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,062,692 November 6,1962 Samuel J. Manganello et a1.

It is hereby certified that error appears in the above numbered patentrequiring correction and that the said Letters Patent should read ascorrected below.

Column 1, line 28, for "ASTM #1" read ASTMJM column 2, line -:29, for"22000 F. read 2200 F. Y

Signed and sealed this 9th day of April 1963.

(SEAL) Attest:

ESTON e. JOHNSON DAVID L. LADD I v Commissioner of Patents AttestingOfficer :UNITED STATES PATENT CFFICE CERTIFICATE OF CORRECTION Patent N3,062,692 November 6, 1962 Samuel J Manganello et a1 It is herebycertified that error appears in the above numbered patent requiringcorrection and that the said Letters Patent should read as correctedbelow.

Column 1 line 28 for "ASTM 1" read ASTM. 4 v

column 2, line x29, for "22000 F." read 2200 F.

Signed and sealed this 9th day of April 1963,,

(SEAL) Attest: I r

ESTON G. JOHNSON DAVID L. LADD V Commissioner of Patents AttestingOfficer

1. A COLD EXPANDED AUSTENITIC STEEL GENERATOR ROTOR COIL SUPPORTRETAINING RING CHARACTERIZED BY A GRAIN SIZE NO COARSER THAN ASTM #4CONTAINING .60 TO .80% CARBON, 8.00 TO 10.00% MANGANESE, .20 TO .60%SILICON, 6.00 TO 7.00% NICKEL, 4.00 TO 5.00% CHROMIUM AND .30 TO .60%COLUMBIUM WITH THE BALANCE IRON AND OTHER ELEMENTS IN AMOUNTS WHICH DONOT HAVE A HARMFUL EFFECT ON THE PROPERTIES.